| Summary: | Previous research has shown that young fishes will decrease foraging activity while in the presence of a predatory threat. In most of these studies, however, individuals have been exposed to acute pulses of predatory threat of short duration; thus, little is known about the long-term impacts of predatory threat on development in newly hatched fish. In the present study, newly hatched ocean pout Macrozoarces americanus were visually exposed to predatory juvenile Atlantic cod Gadus morhua for 6 h per day during the feeding period. At 3°C, 8 wk old pout not exposed to predators were significantly larger (standard length and wet mass), and had a higher hepatosomatic index than fish exposed to predators. Pout exposed to predators also had lower levels of whole-body phospholipids and triacyl-glycerol, as well as decreased levels of essential fatty acids (arachidonic acid and eicosapentaenoic acid). Interestingly, there were no differences in size, hepatosomatic index or lipid content between the 2 treatments when the experiment was performed at 8°C, despite a decrease in foraging activity of the pout exposed to predators at this temperature. These results suggest that frequent predatory threat can affect the development of newly hatched fishes, and that temperature can affect the ability to observe growth trade-offs when performing threat-sensitive foraging experiments with ectotherms.
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